通过(键驰豫)理论, (DFT, TB)计算,与(XPS, workfunction, Raman,vacuum melting, TEM, AFM elasticity measuremts 等)实验的结合,我们获得如下系列自洽的结果和认知,仅供有共同志趣的同仁切磋分享: 1。 C-C 键随原子配位数的降低而自发变短(by =30%) 和增强(by =160%)。 2。 键长和键能的驰豫导致电荷、能量和质量的局域致密和钉扎以及边界非(悬)键单电子的极化. 3。 单键力常数可达1000 eV/m; 德拜温度从金刚石的2000K降至600K。 4. 体弹模量由金刚石的1.0 TPa增至 2.6 TPa;熔化温度从金刚石的3800K降至1593K.单层有效厚度为 0.142 nm。 5。 扶手椅形和重构锯齿形(5,7 原子环)边界的石墨烯的半导体特性源于准双键在最近邻(长度为d)的边界原子间的产生。 6. 锯齿形边界的石墨烯和原子空位的金属特性及狄拉克费米子的选择性产生源于边界等距(长度为sqrt(3)d)悬键电子的极化。 7. 狄拉克费米子具有非零自旋(未对电子),弱结合能(极化杂质态)、极小的有效质量和极大的群速度。 8. 由于弱作用,狄拉克费米子既不显著贡献哈密顿量又不占据哈密顿量所确立的色散关系而是狄拉克色散。 9. 氢原子与悬键电子结合成键淹没狄拉克费米子。 10. 纳米碳管可近似为无边界的石墨烯。 11. 所有这些皆起源于泡令-歌德施密特的“原子半径随配位数减少而收缩”的原理及其拓展 - 键弛豫理论。 12. 有关拉曼和选区XPS研究正在深入,结果待续。 尤其值得关注的是: 13. 边界极化态可能带来更多让人费解的新奇特性,有如超导,热电,拓扑绝缘体,等 - 期待中 。。。 14. 从键与非键的形成,断裂,振动,弛豫以及相应的电子转移,极化,局域化和致密化的动力学过程以及对材料物性的角度出发进行材料科学研究可能成为必然。 主要参考文献: http://www3.ntu.edu.sg/home/ecqsun Underneath the fascinations of carbon nanotubes and graphene nanoribbons. Energy Environmental Science, 2011; 4: 627-655. Discriminative generation and hydrogen modulation of the Dirac-Fermi polarons at graphene edges and atomic vacancies. Carbon, 2011; doi:10.1016/j.carbon.2011.04.064. Graphene nanoribbon band-gap expansion: Broken-bond-induced edge strain and quantum entrapment. Nanoscale, 2010; 2: 2160-2163. Dominance of Broken Bonds and Unpaired Nonbonding pi-Electrons in the Band Gap Expansion and Edge States Generation in Graphene Nanoribbons. J Chem Phys C, 2008; 112: 18927-18934. Coordination-Resolved C-C Bond Length and the C 1s Binding Energy of Carbon Allotropes and the Effective Atomic Coordination of the Few-Layer Graphene. J Chem Phys C, 2009; 113: 16464-16467. Dimension, strength, and chemical and thermal stability of a single C-C bond in carbon nanotubes. J. Phys. Chem. B, 2003; 107: 7544-7546.
pdated 17/10/2011 by Li Lei 1. 低配位原子间短而强的键会引起芯电荷的局域电子钉扎 , 产生正的深能级移动 ; 2. 紧束缚高密度芯电子会使在价带顶部的非键电子(如碳的π电子和贵金 s 轨道上的半满电子)极化,产生负的浅能级移动; 3. 低配位诱导正的芯能级移动,芯能级移动的大小正比于平衡状态下的单键能; 4. 配位数越低扎钉效应产生的极化效应也越明显; 5. 量子钉扎和电荷极化相互耦合会产生新的能态和价带劈裂; 6. 由于 W 边缘的价带同 Rh 吸附原子和 Ag/Pd 合金相似, W 可代替它们作为施主型催化剂; 7. 通过 ZPS 的方法可以得到,当 Re 吸附氧时,由于 O-Re 键能更强,所以芯能级会向深能级移动。 XPS revelation of W edges as a potential donor-type catalyst http://www.ntu.edu.sg/home/ecqsun/RTF/PCCP-W-edge.pdf Atomic Scale Purification of Re Surface Kink States with and without Oxygen Chemisorption http://www.ntu.edu.sg/home/ecqsun/RTF/JPCC-Re.pdf Purified rhodium edge states: undercoordination-induced quantum entrapment and polarization http://www.ntu.edu.sg/home/ecqsun/RTF/PCCP-Rh-edge.pdf
Evidence for a general mechanism modulating carrier lifetime in SiC Physical Review B 81,233203 (2010). 博士期间从事的是半导体方面的研究,材料主要是SiC与Si半导体。从选择这个课题开始,自己头脑中就有一个大概的认识,以后的研究将主要是应用物理方面的。这个认识从某种程度上圈定了以后发文章什么的,最好的也只能往Appl Phys Lett和J Appl Phys等等应用物理类杂志去投稿;有点物理现象内涵的,倒可以向Phys Rev Lett和Phys Rev B去碰碰运气;像纳米方面的高影响杂志,几乎不可能或者非常非常的难。 在做实验的过程中,发现采用电子线辐照的方法可以在SiC中生成一种很理想的Stacking fault,没有任何interface roughness和composition difference,参照下图,而且实验验证这种stacking fault是一直很理想的量子阱结构。其中夹杂着一个很有趣的物理现象:少数载流子的寿命minority carrier lifetime这些Stacking faults上得到了增强。一般都认为Stacking faults是一直缺陷,而缺陷是减少少数载流子寿命的。当发现这个现象后,老板很高兴,说可以投Nature Mater。说实话,自己还非常认认真真的准备了一番,从Nature Mater的写作格式到前前后后的讨论,花了大概一年多。后来投出去了,得到的却是编辑的据信: Dear Mr Chen, Thank you for submitting your manuscript "Post-growth designing the ideal quantum well structures through defect engineering" to Nature Materials, which we regret we are unable to publish. Because there is intense competition for space within the pages of Nature Materials, we must decline a substantial proportion of manuscripts without sending them to referees, so that they may be sent elsewhere without delay. Decisions of this kind are made by the editorial staff when it appears that papers are unlikely to succeed in the competition for limited space. Among the considerations that arise at this stage are a manuscript's probable interest to a general materials research readership, the pressure on space in the various sub-disciplines of materials research covered by Nature Materials and the likelihood that the manuscript would seem of great topical interest to those working in the same or related areas of materials research. And I am sorry to have to say that we must take this view in the present case. We certainly recognize that this is an interesting work and we agree that your demonstration of a quantum well in SiC generated by the electron beam induction of stacking faults deserves rapid publication in some venue. However, although we feel sure that your results will be of interest and value for other specialists, I regret to say that we cannot conclude that the manuscript provides the sort of fundamental advance in general understanding or technological capability that would be likely to excite the immediate interest of a wide audience of materials scientists. Therefore, we feel that the paper would find a better outlet in a more specialized journal, rather than Nature Materials. We are sorry that we could not be more positive on this occasion, but we thank you for your interest in the journal. Please note that our decision does not reflect any doubts about the quality of the work reported, and I hope you will rapidly receive a more favourable response elsewhere. 收到据信,心里自然不是好过,毕竟准备了那么多时间,但现实也只能是move on呢。由于本文含有有趣的物理现象,我们最后决定投Phys Rev B试试。刚开始的几天,也是在等待编辑的审判,后来查询论文状态,写的是在审稿中,说明第一关prescreen已经过了,心里也安心了一些,然后就是漫长的等待。 大概一个月后,收到了编辑的来信,共有三个referee的评价。其中2个评价非常高,另外1个也给了比较好的评价,但提出了一些修改意见。我们及时的按照审稿人的意见修改好,送了出去。没过几天,就收到了编辑的接受信。现在回首起来,感觉工作好好做,认真采纳审稿人的意见,能做的务必做好,不能做的诚恳的说明原因,最后一定会有好的结果的。
近日,读到 JASIS ( 2010 年第一期的第一篇文章) Problems of Citation Analysis: A Study of Uncited and Seldom-Cited Influences ,对我的启发十分大,开始彻底颠覆我并不牢固的情报学基础认识,因此,我把我及时的感受写出来与大家分享,希望能够得到科学网前辈们的指点。 作者: M.H. MacRoberts and B.R. MacRoberts 全文: Problems of Citation Analysis: A Study of Uncited and Seldom-Cited Influences Problems of Citation Analysis: A Study of Uncited (论文下载仅作为学术用途) 一、 读文感受 文章提到了 引文分析的基础 : Cole and Cole (1972) found that highly cited physics papers also cited highly cited papers, and so on. If we did not know that biogeographic papers cited very few of their influences, we might come to the same conclusion as the Coles: that only a small number of individuals contribute to scientific progress. But knowing that the vast majority of influence is not cited and that influence is not to be found in the Thomson Reuters-monitored journals leads to a different conclusion: that manynot a fewcontribute to scientific progress. Cole 在 1972 年发现 高被引的物理学论文同样也会应用高被引论文等等 如果我们不了解生物地理学论文引用很少的对文章产生巨大影响的文献,我们可能得出与 Cole 相同的结论:仅有少数的个体对于科学的进步是有贡献的。但是,如果我们知道大量有影响的内容不会被 SCI 所引证,也许会导致一个不同的结论:是许多个体 而不仅仅是少数人 对于科学的进展有贡献。 (一) 举了两个例子: 1. The latitudinal gradient of species-area relationships for vascular plants of North America. published in 2007 in American Naturalist 一文中引证了 A total of 1,742 floras of North America north of Mexico ( 1742 种植物群),而这些植物群的资料范围覆盖了政府文献、论文、未出版的报告、网页内容、短评以及 2000 多页的参考资料。这部分内容也被提及,出现在 Appendix A ,然而该论文仅引用了 85 篇文献,而这些被引文献仅仅是 SCI 文献,这些文献主要是用于解释物种的多样性的文章。 2. 作者本人发表了一篇 2 页的短文 Palhinhaea cernua (L.) Vasconcellos Franco (Lycopodiaceae) new to Texasin Phytologia ,该期刊不是 SCI 论文。这篇文章通过 SCI EXPANDED 和 GOOGLE SCHOLAR 检索均发现没有任何引证,然而,这篇文章确被整合进了德州和北美的植物地理文献中,该信息被广泛的应用;另外, USDA 植物数据库以及自然服务( NATURESERVE )数据库都将该文章的研究纳入进去。换言之,该论文即被印刷版也被电子版的出版物所引用,这篇文章的研究目的已经达到了。 上面两个例子证明了,被引文献仅仅只能代表有影响文献资料的一个片段。 (二) 作者同样做了一个小的定量实证:(哈哈!虽然作者认为定量分析并不是一种包打天下的方法) We selected 10 theoretical/analytical biogeographical articles that were published in journals that are monitored by Thomson Reuters and examined their bibliographies. These 10 articles are from the 22 described in this study. We recorded whether the cited item was (a) a article from a journal not monitored by Thomson Reuters, (b) an article from a Thomson Reuters-monitored journal, (c) a book or chapter in a book, (d) an unpublished report, (e) a thesis or dissertation, or (f) an online Web source or CD-ROM. There were 530 citations in these 10 articles. We selected five data articles or sources used for data in the 22 theoretical/analytical articles, such as those listed in McLaughlin (2007). We recorded the same information that we recorded for the other sample. We stopped when we reached 530 items so that the two samples would be equal. Table 1 shows the data for the two groups. Statistical comparison of the two groups shows that there is no possibility of them being derived from the same population. Theoretical/analytical biogeographical articles predominantly cite theoretical/analytical articles from Thomson Reuters-monitored journals; data articles do not cite many Thomson Reuters-monitored articles but instead cite work from journals not monitored by Thomson Reuters, unpublished reports, theses/dissertations, and the grey literature. 对于两个群体的统计比较显示:理论或者分析类的植物地理文献主要引用了 SCI 的理论和分析文献;而数据类型的文献则没有引用太多的 SCI 文献,相反,他们主要引用的是非 SCI 文献、未发表的报告、研究论文,或者是灰色文献。 er二、反思 这篇文献对我的震撼是极大的。 主要有二点: (一) 以引文为基础的方法是不是对于所有学科的评价都有价值,是值得反思的。其实,自然科学中,除了植物地理学以外,很多学科的研究都包含了对于原始数据和基础理论分析的研究,而我们现在评价体系的一个重要指标 引文则是对于数据研究这部分内容的价值忽略了的。 (二) 文献计量学中 Cole 的理论:仅有少数的个体对于科学的进步是有贡献的 或者还应该包括 洛特卡定律 这些理论都从 分析方法(仅仅考虑第一作者) + 分析框架(仅仅展示核心作者) + 分析目的(评价作者贡献) 是出于一种狭隘、自私的学术观点。但是,如果我们反思 真的是只有小部分人对于科学的进步有贡献吗? 真的是一将功成万骨枯吗? 。这是我们图书情报学界急需要考虑的问题。 中国的情报学目前还从创作过自己有价值的理论,但研究中确充斥着各式各样标榜自己学术地位的所谓学科知识地图,这有时是一种讽刺。
缺陷对氧化锌的光学、光电子学性能有着非常显著的影响。数十年来,ZnO可见发光的缺陷机制一直存在争议,缺乏统一的理论解释。 近年来,我们发展了具有局域瞬态极端条件的液相激光烧方法,并进行纳米颗粒的独特微结构相关的物性研究。在此基础上,获得了具有稳定较强蓝色发光的氧化锌纳米颗粒,进行了对缺陷发光机制的探索。一方面,研究了蓝色发光对激发波长依赖性。发现:1,蓝色发光存在几个固定的择优发射能量点;2,蓝色发光到绿色发光的转变,不是连续移动而是此消彼长的过程;3,蓝色发光的激发谱可以延伸到可见光波段,相应激发能量明显小于带隙宽度,并存在一系列子峰。另一方面,对相关缺陷进行了电子顺磁共振和正电子湮灭的研究。观察到间隙锌、空位氧、间隙锌复合缺陷、间隙氢在一定条件下的共存;随着蓝色发光到绿色发光的转换,间隙锌和空位氧在EPR谱中存在强烈相关的变化。此外,通过更细致的微结构控制,可见发光获得了一定称度上的调控。 该工作将有助于氧化锌可见发光的最终确立,推动相关基础研究与应用;同时也指出,相对于通常所注意的形貌、尺寸等,纳米材料的微结构控制对其性能具有及其重要的意义。相关论文发表在Adv. Funct. Mater. 2010, 20.561-572.上。该工作得到了国家自然科学基金的资助。 网络链接如下: http://www3.interscience.wiley.com/journal/123237358/abstract Blue Luminescence of ZnO Nanoparticles Based on Non-Equilibrium Processes: Defect Origins and Emission Controls By Haibo Zeng,* Guotao Duan, Yue Li, Shikuan Yang, Xiaoxia Xu, and Weiping Cai High concentrations of defects are introduced into nanoscale ZnO through non-equilibrium processes and resultant blue emissions are comprehensively analyzed, focusing on defect origins and broad controls. Some ZnO nanoparticles exhibit very strong blue emissions, the intensity of which first increase and then decrease with annealing. These visible emissions exhibit strong and interesting excitation dependences: 1) the optimal excitation energy for blue emissions is near the bandgap energy, but the effective excitation can obviously be lower, even 420nm (2.95 eVEg¼3.26 eV); in contrast, green emissions can be excited only by energies larger than the bandgap energy; and, 2) there are several fixed emitting wavelengths at 415, 440, 455 and 488nm in the blue wave band, which exhibit considerable stability in different excitation and annealing conditions. Mechanisms for blue emissions from ZnO are proposed with interstitial-zinc-related defect levels as initial states. EPR spectra reveal the predominance of interstitial zinc in asprepared samples, and the evolutions of coexisting interstitial zinc and oxygen vacancies with annealing. Furthermore, good controllability of visible emissions is achieved, including the co-emission of blue and green emissions and peak adjustment from blue to yellow. 氧化锌纳米颗粒的发光与激发光谱 建议的缺陷发光机制、可见发光调控 发表后记: 对这项工作与这篇文章颇有些感慨。 从工作的开始到发表历时是我至今最长的。这是在我博士工作基础上的继续,留所2年主要精力就花这上面了。当然,还有部分数据没发表。这是个科学问题探索型的基础研究,历程如下。随着对领域认识的不断加深,逐渐对领域内有哪些主要问题、研究状况有了自己的认识。慢慢的,有了解决其中一个(其实就目前潮流而言,是既不新也不热了)的冲动。随后就是独立设计方案,实施试验,进行分析。期间,少不了再学习、再调整、再实施。再后来,数据逐渐积累多了,就自然进入到思考与分析方面,体会数据,体会内涵,体会关联方面,真是所谓殚精竭虑!最后是,逐渐形成了一点自己的观点,就有加入了求证-再试验-分析的循环中。 相反,最后发表到好像没什么故事。本准备好被AFM拒稿后转投物理类IF稍低的杂志的,没想到很快收到的意见都较好,直接接受了。接受后,好像也没什么太高兴的。 自己评价:这是我至今比较好的工作,历史可能会证明观点是错误的,不过我也没什么遗憾的! 这个过程增加了我对科研,对科研中的自己的认识: 1, 认真做点科研,真是不容易!(反之,我的有些文章并没有这么辛苦) 2, 如果能认真做点科研,也不错啊。 3, 要边做边学边提高。 刚才看到关于这篇文章的报道出现在科学网论文栏的头条,有点吃惊。感谢编辑或者朋友的推荐。为了方便感兴趣的朋友的获取,特将文章的PDF文件附上。 文章的PDF文件